Operation; Slide Calibration - Capacity Slide Valve Potentiometer - Emerson Vilter Vission 20/20 Operation And Service Manual

Section 24 • Twin Screw Control

Operation

Once the twin screw is confi gured, its operation is
very similar as the single screw and all options that
are available for single screw confi guration are also
available for twin screw. The only operational differ-
ence is the manual mode of operation. Twin screw
compressors can experience leaky slide seals that can
cause the capacity slide to drift after it has been po-
sitioned by the controller. To counteract the capacity
slide drift problem, the twin screw manual mode op-
eration has an added anti-drift feature that automati-
cally maintains the position of the hydraulic actuator.
Slide Calibration - Capacity Slide Valve
Potentiometer
This section provides critical information and control pa-
rameters related to the capacity slide actuator. The "%
cap" display shows the actual value in percent of the ca-
pacity slide with out any conditioning that might be ap-
plied to the other capacity position displays. In addition,
this section displays the value of the actuator signals
in millivolts in the "input Value" display box, see Figure
24 – 2
Figure 24-2. Slide Calibration - Twin Screw Control
Vission 20/20 • Operation and Service Manual •Vilter/Emerson • 35391SC 1.9
24-2. Slide Valve Calibration - Twin Screw Control.
"-" Button:
• When the operator presses and holds this button,
the output associated with capacity slide decrease
is energized. If the actuator does not turn in the cor-
rect direction when this button is pressed, then the
operator will have to alter how the actuator is wired
to the panel.
"+" Button:
• When the operator presses and holds this button,
the output associated with capacity slide increase is
energized. If the actuator does not turn in the cor-
rect direction when this button is pressed, then the
operator will have to alter how the actuator is wired
to the panel.
Software limit setpoint:
• The Vission 20/20 uses the "Min Limit" and "Max
Limit" setpoint to defi ne an area within the mechani-
cal stops for normal slide travel. These software limits
purpose is to prevent the slide from actually hitting
the mechanical stops which could result in a number
of undesirable consequences. By default, the soft-
ware limits are set to 150mV from either end point.